1. Field of the Invention
The invention relates generally to disk drives, and more particularly to disk drive head assemblies.
2. Description of the Prior Art
As computers have improved over recent years the need for increased data storage has risen dramatically. To meet this need several approaches have been taken to make disk drives capable of storing more data without increasing, and in some cases actually decreasing, their overall size. One approach has been to raise the recording density of the disks by storing more data on the same size disk. Another approach has been to increase the number of disks in the drive's disk stack by spacing the disks closer together.
Increasing the recording density primarily depends on reducing the amount of disk space needed to store each bit of data. A disk drive stores and retrieves data by using a magnetic head which writes data onto the disk by aligning magnetic poles in the magnetic material and reads data by sensing the alignment of previously written poles. The smaller the poles can be made, the more data that can be stored on the disk. However, as the poles are made smaller, the magnetic fields produced by the poles become weaker. Thus, to align and sense the poles, the magnetic head has to be kept very near the surface of the disk.
In order to position magnetic heads sufficiently close to the surface of disks, the heads are typically mounted to air bearing sliders. An air bearing slider is a device which is specifically shaped so that when placed into the airstream existing near the surface of a rotating disk, the slider will provide a lifting force, to cause it to fly just above the disk surface. As magnetic heads are normally much smaller than sliders, they can be mounted to and flown along with the slider. This allows the distance between the magnetic head and the disk surface to be kept relatively small and constant.
Usually, the slider is part of a head gimbal assembly which is attached to an actuator or support arm. As the support arm reciprocates, the slider is moved across the disk surface to precise positions over individual data tracks on the disk. The head gimbal assembly includes a pivot point and a flexure. As the name implies, the flexure is ordinarily a flexible piece of metal, which is stiff enough to urge the slider to maintain a desired position relative to the disk surface, but flexible enough to allow the slider to pitch and roll about the pivot point. It is important that the slider can move about the pivot point so that the slider can freely fly above the disk.
Unfortunately, flying a slider close to the disk surface increases the potential for damage caused by the slider contacting the disk surface. Contact between the slider and disk can result from a shock, jolt or bump to the disk drive, or from the process of loading and unloading the slider between uses. Depending on the flying height of the slider, even a relatively minor shock can displace the slider enough to cause it to collide with the disk surface. Also, an external shock or jolt to the disk drive can cause structural damage to the flexure if the slider is displaced too far about, or from, the pivot point or if the flexure is loaded excessively. Such shocks or jolts can also occur during the manufacturing process when the disk drive is assembled. Damage to the flexure can include dimple separation and bending of the flexure. Dimple separation can occur if the flexure/slider assembly separates too far from the pivot point and deforms the flexure into its plastic range. With dimple separation the flexure no longer can maintain the slider in contact with the pivot point or even if contact can be maintained it cannot be done with the same resiliency.
Thus, to allow for the low flying heights required to achieve higher recording density, an apparatus is needed which will limit or prevent damage caused by shocks, jolts or bumps. However, such an apparatus should also allow for load/unload operations.
To increase recording density and to improve the head-disk interface (to reduce wear to the slider and surface of the disk and to reduce stiction between the slider and disk), load/unload operations have been employed. As the name implies, a load/unload operation involves unloading and loading steps. The “unload” portion of a load/unload operation involves physically lifting and retaining the head gimbal assembly (with the slider) up and away from the surface of the disk. Unloading is done to keep the slider from contacting the surface of the disk when the disk is slowed to a stop. Without unloading, as the disk slows to a stop, the airflow over its surface will lessen and the slider will stop flying. At this point, the slider will drop to contact and rest upon the disk surface. Slider contact with the surface of the disk causes both the slider and the disk surface to sustain some wear. Further, with the slider resting on the disk, when the disk is spun up again there will exist stiction between the slider and the surface of the disk. Stiction may cause structural damage to the delicate head gimbal assembly. Stiction causes further wear of the slider and disk surface as well as the load on the motor turning the disk.
During the “load” portion of the load/unload operation the head gimbal assembly is lowered down from its rest towards the disk. With the disk spinning sufficiently, the slider will begin flying as it is lowered to the surface of the disk.
Load/unloading can occur by having a tab on the head gimbal assembly which contacts and is lifted by, a load/unload ramp. As the tab is moved along the ramp it is raised increasingly further up from the disk surface. This in turn raises the slider up from the surface and allows the disk to be stopped without the slider landing and resting on the disk surface.
The other approach to increasing the overall disk storage has been to increase the number of disks in the disk drive's disk stack. However, as additional disks are added to the stack, the spacing between the disks decreases. Therefore, the disk spacing can only be decreased a certain amount. This amount is determined by the height of the portion of the head gimbal assembly which must fit between the disks.
In a disk drive having a load/unload ramp, the space between disks is limited by the height of lifter tabs of the head gimbal assemblies. Specifically, the height of the head gimbal assembly is defined by the amount which the lifter tab projects above the rest of the gimbal assembly. The lifter tab rises relative to the test of the head gimbal assembly to allow access by the load/unload ramp. As such, the height of the lifter tab directly limits the spacing between disks, which in turn limits the disk stack density. Therefore, a need exists for a head gimbal assembly with a low overall profile.
Thus, a head gimbal assembly with improved head-disk interface is sought which will permit increased data storage by allowing for both greater recording density and closer disk stacking. To provide increased recording density without increasing damage caused by contacts of the slider to the disk caused by external shocks or jolts, the head gimbal assembly must employ an apparatus to limit the slider's motion. Also, the profile of the head gimbal assembly must be low enough to allow the disks in the disk stack to be placed closer together to increase the stack density. However, the head gimbal assembly must still be capable of load/unload operations to reduce slider-disk wear and stiction.